Position-insensitive mercury relay

ABSTRACT

A miniature mercury switch, comprising an enclosure including a tube having a mercury wettable inner surface, within which a contact carrying shuttle is movable along the axis of the tube. The shuttle is not mercury wettable except for a slot or groove extending between its ends and for contact surfaces at its ends, but it rides on a mercury layer attached to the inner surface of the tube. Secured within and extending into the ends of the tubes are unwettable rods of magnetic material having stationary end contacts which are mercury wettable. The contacts on the shuttle ends include tantalum or niobium spacers extending beyond mercury wettable end contact surfaces on the shuttle, the spacers accepting the impacts when the relay contacts operatively close, which implies that the wettable contact areas on the shuttle ends closely approach the stationary end contacts, so that the mercury layers coalesce, but the wettable surfaces do not impact. The quantity of mercury within the enclosure is only sufficient to form a layer of mercury on the mercury wettable surfaces within the enclosure, but insufficient to form a pool of mercury, or to cover unwettable surfaces while wettable surfaces are covered, and the slot or groove in the shuttle facilities transfer of mercury from end to end of the enclosure, which prevents pooling at either end of the enclosure concomitant with depletion at the other, due to imbalance of mercury transfer during relay operation. Stationary contacts are, for open contact condition, spaced from movable contacts, by mercury unwettable surfaces of the enclosure, and the quantity of mercury available is insufficient to cover these unwettable surfaces and also to form a mercury layer on the mercury surfaces.

United'States Patent [1 Bitko 11 Jan. 15, 1974 POSITION-INSENSITIVEMERCURY RELAY [75] Inventor: Sheldon S. Bitko, Cherry Hill, NJ.

[73] Assignee: Fifth Dimension Inc., Princeton,

[22] Filed: Nov. 1, 1972 [21] Appl. No.: 302,677

Related 0.8. Application Data [60] Division of Ser. No. 71,294, Sept.10, 1970, Pat. No. 3,715,546, which is a continuation-in-part of Ser.No. 880,128, Nov. 26, 1969, Pat, No. 3,644,693.

[52] US. Cl 200/214, 200/210 Primary ExaminerHerman J. HohauserAttorney-Hyman Hurvitz [57] ABSTRACT A miniature mercury switch,comprising an enclosure including a tube having a mercury wettable innersurface, within which a contact carrying shuttle is movable along theaxis of the tube. The shuttle is not mercury wettable except for a slotor groove extending between its ends and for contact surfaces at itsends, but it rides on a mercury layer attached to the inner surface ofthe tube. Secured within and extending into the ends of the tubes areunwettable rods of magnetic material having stationary end contactswhich are mercury wettable. The contacts on the shuttle ends includetantalum or niobium spacers extending beyond mercury wettable endContact surfaces on the shuttle, the spacers accepting the impacts whenthe relay contacts operatively close, which implies that the wettablecontact areas on the shuttle ends closely approach the stationary endcontacts, so that the mercury layers coalesce, but the wettable surfacesdo not impact. The quantity of mercury within the enclosure is onlysufficient to form a layer of mercury on the mercury wettable surfaceswithin the enclosure, but insufficient to form a pool of mercury, or tocover unwettable surfaces-while wettable surfaces are covered, and theslot or groove in the shuttle facilities transfer of mercury from end toend of the enclosure, which prevents pooling ateither end of theenclosure concomitant with depletion at the other, due to imbalance ofmercury transfer during relay operation. Stationary contacts are, foropen contact condition, spaced from movable contacts, by mercuryunwettable surfaces of the enclosure, and the quantity of mercuryavailable is insufficient to cover these unwettable surfaces and also toform a mercury layer on themercury surfaces.

3 Claims, 6 Drawing 1F igures PATENTEDJAN 15 m4 MERCURY 7 LAYEE ZFIG.4

1 POSITION-INSENSITIVE MERCURY RELAY CROSS REFERENCE BACKGROUND OF THEINVENTION This invention is an improvement of the relay disclosed in U.S. Pat. to Donath, U. S. Pat. No. 3,144,533, issued Aug. 11, 1964. Thatpatent includes a non-wettable shuttle riding on a layer of mercury sustained by the inner mercury wettable surface of a metallic tube. Thecontacts of the relay are mercury wettable, one at each end of the tube,each contact coacting with mercury wettable contacts formed on the endsof the shuttle. It is found that after long shelf life or many closuresof the Donath switch the contacts of the Donath relay tend to stick, thenumbers of trouble-free operations decreasing with increase oftemperature. Study of the mechanism of sticking indicates that it iscaused by diffusion of metal between contacts clue to proximity orcurrent flow, and that this occurs despite the mercury layers on thecontacts and perhaps be cause of it, since mercury wettable metal tendsto be soluble in mercury. All attempts to discover metals which whilemercury wettable and therefore suitable as contacts, are also totallynon-soluble and nontransferable under proximity or current flow were unsuccessful.

The concept was then advanced of including in each of the shuttlecontacts an impact absorbing spacer which is non-mercury wettable, andhence not soluble in mercury, but sufficiently hard to absorb impactwithout substantial deformation. The contacts themselves must bewettable, but these are located so far inward of the spacers that amercury layer attached to the shuttle contact can reach the mercurylayer attached to the stationary contact, yet are so located that noimpact or transfer of metal occurs between the mercury wettablesurfaces. This concept is broadly disclosed and claimed in Bitko, Ser.No. 880,128, supra, as applied to a reed switch or relay. The presentinvention relates to the same broad concept as does Ser. No. 880,128,but applied to a shuttle relay, and includes novelty in respect to thefabrication and structure of the shuttle. The envelope is designed topermit of particularly economical assembly from simple parts.

SUMMARY OF THE INVENTION A mercury relay having a shuttle armatureriding on a thin layer of mercury, in which the ends of the shuttle aremercury wettable but provided with non-mercury wettable projectionswhich provide spacing to stationary contacts and thus prevent contactsticking.

BRIEF DESCRIPTION OF THE DRAWINGS The above and still further objects,features and advantages of the present invention will become apparentupon consideration of the following detailed descrip' tion of onespecific embodiment thereof, especially when taken in conjunction withthe accompanying drawings, wherein:

FIG. 1 is a new partly in side elevation and partly in section of arelay according to the invention;

FIGS. 2-5 are sections taken through a solid cylinder of material atvarious stages in the fabrication of a shuttle for the relay of FIG. 1;

FIG. 6 is a broken away view in side elevation illustrating details ofcontacts of the relay of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT The relay of FIG. 1 is providedwith two stationary contact bearing rods 1 and 2, the contacts beingstationary and extending into a sealed envelope 3. Rods 1 and 2 arefabricated of non-mercury wettable magnetic material but each endsurface is provided with a coat ing or layer 4 of mercury wettablematerial such as platinum. The thickness of the coating or layer may beabout 0.0002 inches. The rod must be relatively hard, to withstandrepeated impacts without deformation, but the coating or layer may berelatively soft, and therefore may suffer deformation.

A glass annulus 5 surrounds each. rod interiorly of the envelope at itsends, and is sealed thereto, providing insulative support.

Interiorly of the envelopes is a thin walled metallic tube 6 of circularcross section, which is metallic and interiorly mercury wettable. Fromthe tube, midway thereof extends an annulus 7, which serves to positionactuating coils 8, 9 and also to position two glass cylinders l0, 11which extend over tube 6 from opposite ends and extend beyond the tube 6at each end of the tube 6, into superposed conjunction with glassannulus 5. The glass tubes 10, 11 are heated to effect a seal with themetallic tube 6 and with the glass annuli 5 and with the metallicannulus 7, and the enclosure is further end sealed by discs 12. Thereby,an enclosure is formed, which is hermetically sealed so that it may befilled with inert gas.

Within the enclosure is located a shuttle 14, having thereon a helicalgroove 15 extending along the entire length of the shuttle. The shuttle114 is generally cylindrical in outline as seen from its end andpresents a sliding fit within the tube 6, making allowance for a thinlayer of mercury 16 intervening between the shuttle and the tube. Theouter surface layer 17 of the shuttle is not mercury wettable. Thehelical groove 15 extends into a non-magnetic but mercury wettable core18, and a tantalum or niobium tube 20, which is not wettable, extendsbetween the outer layer of the shuttle and the inner core. The grooveprovides a path for interchange of mercury between the ends of theenvelope, which is required to assure balanced distribution of mercury,at least statistically. If the groove is not provided, mercury maycollect in one side of the switch, resulting in a short at that side andpossible dry contacts on the other side. The groove also conveys mercurywhich is integral with or joined with that existent in the thin layer onthe tube 6, thereby to provide a low resistance path directly from thecore 18 of the shuttle to the outer tube.

The shuttle requires, at each of its ends according to the presentinvention, an interposer 21 between the movable contact surface 22,which is mercury wettable and always is provided with a layer of mercury23, and the stationary contact surface 4, which also is mercury wettableand is provided at all times with a layer of mercury 24. The interposeris, for optimum results, an annulus of either tantalum or niobium, butmay consist of other mercury non-wettable hard metals if these aresufficiently hard, which extends beyond the true contact surface 22 byabout one mil. While the interposer 21 may be fabricated in a variety ofways, a preferred way is to remove an annulus 25 of the outer end oftube 21, exposing a ring of the interposer metal, and thereafterexposing the interposer metal to a hot hydrogen atmosphere. Thistreatment causes the interposer metal, if tantalum or niobium, to expandby absorption by hydrogen. However, it is also feasible to remove alayer of metal from the core 15, as by dissolving it in hot mercury. Ineither case, the interposer is produced as a projecting annulus, whichimpinges against the contact surface 19 when the contacts close. Theinterposer metal, being mercury non-wettable, cannot diffuse into themercury. The layer 19 is relatively soft, and quite thin, while theinterposer is relatively hard, so that relatively few operations of therelay produce an annulus recess 26, extending through the layer 4. Theinterposer 21 is slightly longer axially than the recess 26 is deep, sothat the interposer always impinges directly on the end of rod 1, whichis itself not mercury wettable. Thereby, the metal layer 4 does notdiffuse on impact, and the relay is free of sticking, indefinitely.

A preferred method of fabricating the slug 14 is to start with acylinder 29 comprising a non-magnetic, mercury wettable core 16,interiorly, an inner tube of tantalum 20, surrounding core 16, and anouter tube of magnetic, non-mercury wettable metal 17, all integral withone another. The cylinder 29 is flattened by rolling, as illustrated inFIG. 3, and cut down along the line 30, as by grinding, to expose theinner core 18, resulting in an elongated member which is generally ovoidfor more than half its circumference and flat for the remainder, theflat surface 31 exposing all three metals. The shape of FIG. 4 isfurther rolled to achieve precise dimensions, and the resultant shape istwisted to form a multi-turn helix, which can be electropolished toprecise OD and length dimensions, and to have an essentially circularoutline as viewed from an end.

The present relay has the operating properties of the Donath relay, plusthe additional property that its contacts do not stick even after manymillions of clo sures. Particularly, it may be mentioned that the switchis inherently bistable, and can therefore be operated in response to ashort impulse which need not endure.

The wettable to non-wettable surface ratio of the Donath switch issubstantially retained and the O.D., length and general operatingcharacteristics may remain as described in the Donath patent, to whichreference is made for a complete discussion of the theory and philosophyof operation.

Thehelical shuttle or slug 14 should preferably be symmetrical inrespect to weight distribution along its length and also in respect todistribution of strip 15, which because it is wettable establishes adrag, and also in respect to the outermost non-wettable surface. Thefirst mentioned objective, i.e. symmetry, is readily achieved by havinga helix of an integral number of turns, in the present case, two.Reduction of the area of the non-wettable surface reduces friction, andcontrolling the depth and width of the inner diameter of 15 of thehelix, which is mercury wettable, affects total shuttle mass, becausemercury is dragged along the shuttle. The presently described method ofmaking the shuttle enables ready control of the several factorsmentioned. There is a problem of so proportioning the dimensions of theshuttle that it is magnetically symmetrical and also symmetrical inrespect to weight distribution, so that on transfer of the shuttle fromone location to another it will ride axially and this in any orientationof the relay, which is totally position insensitive. This isaccomplished by employing an integral number of helical turns, andconformity of structure along the length of the slug.

It will be appreciated that core 15 need not be nonmagnetic.

While I have described and illustrated one specific embodiment of myinvention, it will be clear that variations of the construction whichare specifically illustrated and described may be resorted to withoutdeparting from the true spirit and scope of the invention as defined inthe appended claims.

I claim:

1. A switch comprising an envelope,

at least two contacts,

a pair of mutually insulated conducting liquid layers within saidenvelope each associated with a different contact surface,

at least one of said contact surfaces being movable toward and away fromthe other of said contact surfaces,

said conducting liquid layers wetting at least said contact surfaces andbeing capable of completing the circuit between said contacts when saidcontacts are operatively closed, the ratio of the total area of thesurfaces within said envelope to the area of said conducting liquidlayers being less than 2,

wherein at least one of said contact surfaces carries an interposerwhich is non-wettable by said liquid and which is positioned anddimensioned to absorb impacts occurring on closures of said contactsurfaces and to maintain a predetermined physical separation of saidcontact surfaces during said closures.

2. A relay comprising an envelope,

a quantity of conducting liquid having high surface tension located insaid envelope,

contact surfaces and surfaces mutually insulating said contact surfaceslocated internally of said envelope,

said contact surfaces only being wettable by said liquid,

said surfaces mutually insulating being unwettable by said liquid,

said surfaces mutually insulating at least in part forming saidenvelope, the quantity of said liquid being only adequate to cover saidcontact surfaces with a layer of said liquid and inadequate to form apool of said liquid in addition to said layer,

wherein at least one of said contact surfaces includes an interposerfacing the other of said contact surfaces,

said interposer being unwettable by said liquid and dimensioned toprevent near approach of said contact surfaces by less than about onemil.

3. The combination according to claim 2, wherein said at least one ofsaid contact surfaces is included on a shuttle freely floating in saidliquid.

1. A switch comprising an envelope, at least two contacts, a pair ofmutually insulated conducting liquid layers within said envelope eachassociated with a different contact surface, at least one of saidcontact surfaces being movable toward and away from the other of saidcontact surfaces, said conducting liquid layers wetting at least saidcontact surfaces and being capable of completing the circuit betweensaid contacts when said contacts are operatively closed, the ratio ofthe total area of the surfaces within said envelope to the area of saidconducting liquid layers being less than 2, wherein at least one of saidcontact surfaces carries an interposer which is non-wettable by saidliquid and which is positioned and dimensioned to absorb impactsoccurring on closures of said contact surfaces and to maintain apredetermined physical separation of said contact surfaces during saidclosures.
 2. A relay comprising an envelope, a quantity of conductingliquid having high surface tension located in said envelope, contactsurfaces and surfaces mutually insulating said contact surfaces locatedinternally of said envelope, said contact surfaces only being wettableby said liquid, said surfaces mutually insulating being unwettable bysaid liquid, said surfaces mutually insulating at least in part formingsaid envelope, the quantity of said liquid being only adequate to coversaid contact surfaces with a layer of said liquid and inadequate to forma pool of said liquid in addition to said layer, wherein at least one ofsaid contact surfaces includes an interposer facing the other of saidcontact surfaces, said interposer being unwettable by said liquid anddimensioned to prevent near approach of said contact surfaces by lessthan about one mil.
 3. The combination according to claim 2, whereinsaid at least one of said contact surfaces is included on a shuttlefreely floating in said liquid.